The invention relates to electronic postage meters and metering systems and particularly to an improved method and apparatus for ensuring the validity of a postal indicia printed by a postage metering system. The term electronic postage meter or metering system as used herein also refers to other similar meters, such as parcel registers and tax stamp meters that dispense and account for value.
Since the days of the first postage meter, security has been considered the heart of postage meter operation. Security must be absolute since monetary value is being printed.
In prior postage meters, an indicia is printed by a letter press utilizing a uniquely engraved die containing postal information, such that the metered postage indicia is traceable to a particular postage meter. Newer postage meters have been developed that include electronically controlled printers, such as thermal printers, ink jet or dot matrix pin printers for printing the indicia. While these newer meters work well in concept, there is a further consideration of security that must be addressed. Such indicias are rather easily printed by anyone who has a computer operating under a suitable program and an appropriate printer. One way of ensuring the validity of a particular indicia has been to encode a message in the indicia such that an unauthorized person cannot reproduce the appropriate encoding.
Such meters utilizing encoded information are disclosed, for example, in U.S. Pat. No. 4,757,537; issued July 12, 1988 to Arno Muller filed Apr. 7, 1985 and in U.S. Pat. No. 4,725,718; issued Feb. 16, 1988, by R. Sansone entitled Postage and Mailing Information Applying System filed concurrently herewith, both assigned to the Assignee of the instant application.
In a system disclosed in U.S. Pat. No. 4,637,051; issued Jan. 13, 1987 of John Clark, filed July 18, 1983, and assigned to the Assignee of the instant invention there is taught another method and apparatus for producing a coded indicia. In this device, the encoding is such that the indicia is printed in human readable format, but the dots forming the indicia are modified by voids or displacements or the like in order to produce a coded message that is then decodable to ensure that the coded information is identical to the human readable information of the indicia.